Rapid curing epoxy resin compositions



United States Patent 3,397 157 RAPID CURING EPOXY RESIN COMPOSITIONSGeorge W. Holmes, Walnut Creek, Calif., assignor to The Dow ChemicalCompany, Midland, Mich., a corpora- Patented Aug. 13, 1968 however, thatthe above compounds are merely illustrative and that other salts orother polyamines may be used provided that the salt and polyamines arecapable of forming a coordination complex which will decompose at a onof Delaware 5 temperature within the range of from about 100 C. to

No Drawing. Filed Nov. 26, 1965, Ser. No. 510,096

8 Cl i (CL 260 2) Dicyandiamide has been useful as a latent curing agentfor all of the common epoxy resins. The polyamine-metallie saltcoordination complexes, as herein defined, may be ABSTRACT OF THEDISCLOSURE used according to this invention to accelerate the cure ofThis invention relates to compositions of matter conany of these.ilcyanihamldfl'epoxy resm.systeins' Amfmg sisting essentially of thereaction products of certain epoxy h epoxy reslns whlch may cured i thlst' resins, a dicyandiamide curing agent and an accelerator non agentsare the polyglycldyl denv2 ltlves of (1) comprising certainpolyamine-metallic salt coordination hydnc phenols; alky} Sub.st1tuteddlhydncphenols; complexes. These compositions are particularly suitablel5 (3) halogen Substltuted dlhydnc Phenols; (4) blsphenols for use asadhesives and coatings and the like Where a represented by the formularapid high temperature latent cure is desired. R1 Ra omer- -01;

Dicyandiamide has been used as a latent curing agent for epoxy resins.There is substantially no reaction be- R2 R4 tween the curing agent andresin over long periods of time where R is selected from the groupconsisting of alkylene, at ambient temperatures. The mixture must beheated to O a temperature of about 165 C. and held at that tempera- [112L ture for an extended period of time to eiTect the cure. The and rateof cure increases with temperatures up to about 200 (5) polyoxyalkyleneglyc l the Condensation P d- 220 C. where the cure is almostinstantaneous. The rate of nets of formaldehyde and phenol, alkylsubstituted phecure can be accelerated or otherwise modified with nolsof halogen substituted phenols; and (7) aromatic amines, amides,quaternary ammonium compounds, and amines; and R R R and R areindependently secertain substituted melamines. lected from the groupconsisting of hydrogen and halogen.

We have found that the cure of epoxy resins with di- Methods by whichthe resins can be prepared are illuscyandiamide can be significantlyaccelerated with certain trated in the following examples.polyamine-metallic salt coordination complexes. Thus, our Example 1invention enables the curing of epoxy resins with dicy- 3r andiamide asa latent curing agent with the ability to dea In each of a serles of e li 100mm y Weight crease the temperature at which the latent curing agentof an P Y resln P P y y y ether of an produces a cure without adverselyaffecting the properties o'cfesol-fofmaldehyde Teslll havlng an Pequlvalent f h cured resin Weight of about 225 and a Durrans meltingpoint of about It is known that various metal salts such as zinc and 40YVa$ adm1Xed Wlth Varymg amounts of p l cadmium halides, foam complexeswith polyamines, such Qwyandmrmde and an -(fi p y y e q asethylenediamine and diethylenetriamine. Such com- Zlfle PXalate f pI1ta1I1 1I1g 63 Pereent fllemme pounds, which are hereinafter referredto as coordination tefmlned y lfltfogen y t F P QE 1:2 complexes, arealso known to be unstable under the incompleX 0f Z1I1C Salt and dlamlne-The fesln mlxtures fluence of h V were cured individually at atemperature of 165 C. and

The coordination complexes contemplated for use by the times Tequ 1redto Cure to a g State, as detel'mlned the present invention are themetallic salts of a polyamine y the eonyel'ltlonel Stroke cure test,Were recordedhaving the general formula The following Table Iillustrates the amounts of dicyandiamide and coordination complexemployed as parts H2N{'CH2 CH2 NH HR r per hundred parts of epoxy resin(phr.) and the stroke Where n is an integer of from 1 to 5 and R ishydrogen, cure time, in seconds, required.

TABLE I (phr.) (phr.) Stroke Cure Sample Number Dicyandiamide Ooord.Complex Time,

Sec. 165

For Comparison:

alkyl, aryl and aralkyl, which complexes decompose rap- Example 2 idlywhen subjected to temperatures within the range or from about -200 C. Asexemplary of suitable metal salts are zinc and cadmium halides, oxalatesor benzoates and the like. Suitable polyamines includes the polyethyleneamines such as ethylenediamine, substituted ethylenediamines such as N-(B -phenethyl)ethylenediamine, and diethylenetriamine. Other suitablepolyamines include dipropylenediamine and piperidine and the like andtheir substituted derivatives. It is to be understood,

TABLE II (phn) (phr.) Stroke Cure Sample Number Dicyandiamide Coord.Complex Time,

See. 165

For Comparison:

Example 3 andiamide is present in amounts sufiicient to provide at leastabout 1 part by weight per 100 parts of said epoxy In each series ofexperiments, varying amounts of a resin, wherein the ratio ofdicyandiamide to polyaminecoordination 901111316X p pared from zincchloride and metallic salt coordination complex is from about 1:1 andethylenediamine containing 51.5 percent diamine, corre- 1:10; andwherein said metallic salt is selected from the sponding to a 1:3complex of zinc salt and diamine, group consisting of zinc and cadmiumhalides, oxalates were added to the epoxy resin of Example 1. Each ofand benzoates, the formulations were then separately spread on two in-2. The composition of claim 1 wherein said polyaminedividual strips of1" x 4" x 0.064 aluminum strips, metallic salt coordination complex isacomplcx of apolywhich strips were then joined by forming a one inch byethyleneamine and said metallic salt. one-half inch overlap joint. Eachof the individual sam- 3. The composition of claim 2 wherein saidcoordinaples was then loosely clamped together and placed in a tioncomplex is a complex of ethylenediamine and zinc circulating air ovenfor a period of 15 minutes with such oxalate.

oven being maintained at a temperature of about 175 C. 4. Thecomposition of claim 2 wherein said coordina- The samples were thenremoved from the oven and left tion complex is a complex ofN-(B-phenethyD-ethyleneat room temperature for a period of three days,and then diamine and zinc oxalate. tested for bond shear strengthutilizing an Instron ten- 5. A process for preparing an epoxy resincomposition sile tester. The following Table III illustrates theformuwhich can be cured rapidly to a thermoset resin which lationsemployed and the bond shear strength observed. process consists ofintimately admixing with an epoxy TABLE III (phr.) (Dhr.) Bond ShearSample Number Dicyandi- Coord. Complex Strength (p.s.i.)

amide For Comparison:

10 10 570 The Invention:

It is apparent from the above data that there is a resin having aplurality of 1,2-epoxide groups per mole pronounced synergistic eifectas regards acceleration of cule a mixture consisting essentially of (a)dicyandiamide cure time when the mixtures of the present invention areand (b) a polyamine-metallic salt coordination complex employed, i.e.,where from 10 to 25 parts of a mixture which is unstable at atemperature of from about 100 of dicyandiamide and coordination complexhaving a to 200 C., wherein said dicyandiamide is present in ratio ofdicyandiamide to complex of from about 1:1 to amounts suflicient toprovide at least about 1 part by 1:10, is admixed with the epoxy resinprior to curing. weight per 100 parts of said epoxy resin, wherein theIt has further been found that the physical properties ratio ofdicyandiamide to a polyamine-metallic salt coof such resins are notadversely affected, as compared to ordination complex is from about 1:1and 1:10, and resin compositions absent the coordination complexacwherein said metallic salt is selected from the group concelerator,and that such resins may be advantageously sisting of zinc and cadmiumhalides, oxalates and benzoemployed in applications where a rapid hightemperaates. ture latent cure is desired. Such resins are particularly6. The process of claim 5 wherein said polyaminesuitable as adhesives,reinforced plastics, coatings, potmetallic salt coordination complex isa complex of a polyting compounds, and the like. Further, it is to beunderethyleneamine and said metallic salt. stood that fillers and otherconventionally employed ma- 7. The process of claim 6 wherein saidcoordination terials may be utilized in the resins of the presentinvencomplex is a complex of ethylenediamine and zinc oxalate. tion forthe desired purposes, and that such resins may 8. The process of claim 6wherein said coordination be prepared, fabricated or applied by anydesired or concomplex is a complex ofN-(fi-phenethyl)-ethylenediaventional technique. mine and zinc oxalate.

What is claimed is:

1. A thermosettable resin mixture consisting essential- References Cited1y of parts by weight of an epoxy resin having a plu- UNITED STATESPATENTS rality of 1,2-epoxide groups per molecule, and from about 10 to25 parts by weight of a mixture consisting essen- 5 2,962,453 11/1960Phllhps et tially of (a) dicyandiamide and (b) a polyamine-metallic saltcoordination complex which is unstable at a tempera- WILLIAM SHORTPrlmary Examl'ler' ture of from about 100 to 200 C., wherein said dicy-T. E. PERTILLA, Assistant Examiner.

